The in-mold coating (IMC) as a mass production process offers potential to generate low-cost, high precision surface qualities on polymeric materials for optical applications, such as mirrors and reflectors. The combination of photo-curable coating systems and the IMC process provides several advantages, especially short curing durations and reduced plant complexity. This work presents the generation of optical precision surface finishes on highly filled bulk molding compound (BMC) substrates by coating with UV-curable epoxy in a closed mold. The influence of process parameters as intensity, radiation dose and film thickness on surface finish and adhesion to the substrate is analyzed. Methods for adhesion improvement, such as surface pre-treatment and substrate modification, are taken into account as well. The curing behavior during the coating process is detected in-situ via dielectrical analysis (DEA).